1. Field of the Invention
The present invention relates to the field of printing and in particular, to systems and methods for performing trapping optimizations in print devices.
2. Description of Related Art
Pixels generated by a color printer typically consist of colors from multiple color planes. For example, in a color printer that uses cyan, magenta, yellow, and black (“CMYK”), a single pixel can consist of color from one or more of the four color planes. A wide range of colors may be produced by a printer when colors from constituent color planes are combined with differing intensities. The color components that make up a pixel are ideally printed on top of, or very close to one another. However, because of misregistration caused by print engine misalignment, paper stretching, and other mechanical imprecisions, the constituent color planes that make up a single pixel may not overlap adequately resulting in unsightly small white gaps between different-colored regions on the page, or in colored edges to black regions. To redress misregistration it is common to use a technique called trapping, which expands or contracts coloring regions slightly in order to eliminate white gaps and/or colored edges between graphical objects. Trapping introduces areas of color into color separations and masks the visible effects of misregistration.
Trapping is often implemented using raster-based trapping, which involves the computationally expensive step of finding object boundaries using data in the frame buffer that potentially spans multiple color planes. In large part, the computational cost arises because trapping may be performed on a pixel-by-pixel basis. When trapping is performed, color typically flows from pixels of higher luminosity in the trapping region to pixels of lower luminosity in the region. Accordingly, there may be a significant processing overhead to determine the luminosity of a pixel and the color contribution of the pixel within the trapping region.
For example, raster-based trapping performed even for a relatively small 3×3 pixel area with width=height=1 using a CMYK color model, involves checking and comparing no less than 36 pixel values (9 pixels across 4 planes) memory locations. Because the computational cost is associated to a large degree with a brute force pixel-by-pixel approach, significant reductions in computational cost may be achieved by reducing the number of pixels processed as potential trapping candidates. Thus, there is a need for systems and methods that decrease the computational cost associated with trapping by providing optimizations for pixel based raster trapping.